The proposed research will utilize tissue culture preparations to study the signals involved in controlling Schwann cell function. Experiments are proposed to study the axonal influences on Schwann cell secretion and the influences of the axon-Schwann cell unit on fibroblast function. Experiments are also proposed to study the axonal changes that occur when a neuron becomes competent to induce myelin formation. Studies in tissue culture will be directed at the problem of identifying products of Schwann cell secretion. The effects of alterations in Schwann cell secretion will be studied by utilizing agents known to either suppress or alter the secretory activity of Schwann cells. We also propose to study the ability of Schwann cells to provide trophic support for neurons. Additional studies are directed at delineating the requirement of Schwann cells on contact with extracellular matrix for the expression of normal Schwann cell function. We plan to continue studies on the mouse mutant dystrophic to test our hypothesis that an abnormality of an extracellular matrix component may explain the peripheral nerve abnormalities in this animal.